[filebeat] Check for duplicate ID for filestream metrics

[taylor-swanson]

What does this PR do?

• If a duplicate ID was used for filestream, set the ID for metrics to an empty string to prevent a panic.
• A valid metrics instance will still be generated, but collection of metrics will not occur.

Why is it important?

Fixes a panic that can occur when a duplicate ID is used.

Checklist

• My code follows the style guidelines of this project
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files
• [ ] I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

Create a config with duplicate IDs, such as:

filebeat:
  inputs:
    - type: filestream
      id: foo
      paths:
        - /tmp/foo
    - type: filestream
      id: foo
      paths:
        - /tmp/foo2
output:
  file:
    enabled: true

Run filebeat. The first instance should register with metrics. Subsequent instances will still register, but with an empty string. This still creates a valid metrics instance, but does not collect and report metrics.

Related issues

• Closes Filestream inputs with duplicated ID cause Filebeat to panic #35964

Logs

filestream input with ID 'foo' already exists, this will lead to data duplication, please use a different ID. Metrics collection has been disabled on this input.

{"log.level":"error","@timestamp":"2023-06-29T16:55:26.299Z","log.logger":"input","log.origin":{"file.name":"input-logfile/manager.go","file.line":183},"message":"filestream input with ID 'foo' already exists, this will lead to data duplication, please use a different ID. Metrics collection has been disabled on this input.","service.name":"filebeat","ecs.version":"1.6.0"}

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @taylor-swanson? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[elasticmachine]

Pinging @elastic/elastic-agent (Team:Elastic-Agent)

[elasticmachine]

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• Start Time: 2023-06-30T18:52:50.989+0000

• Duration: 69 min 29 sec

Test stats 🧪

Test	Results
Failed	0
Passed	7996
Skipped	757
Total	8753

💚 Flaky test report

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[VannTen]

It looks like this did not completely fix the issue, see #35964 (comment)